The things I know about tasklet:

1. Tasklet runs with all interrupt enabled.
2. The tasklet runs in interrupt context.
3. It can't be sleep.
4. It runs in atomic way.
5. It has the assurance to be scheduled never late than next tick.

My questions:

1. Since in bottom half all interrupts are enabled, what happened If a tasklet is running and in between any interrupt comes. (If interrupts are
disabled during tasklet execution then what is the benefit of tasklet)?

2. Why is the surety that tasklet will always be scheduled upto next tick?

3. Is it correct to say that tasklets are softirq with priority level 0(Hi priority tasklet) and priority level 6(Normal taslet)?

What is a tasklet? Is it related to any window manager in particular?

tasklet is bottom half mechanism to defer the work later in linux.

It's to do with interrupt handling in the kernel. There's plenty of detail on google, here's a brief one: tasklets.